JP4652725B2 - Photomask defect correction method - Google Patents

Description

  The present invention relates to photomask defect correction using a combined device of a focused electron beam device and an atomic force microscope.

  With the miniaturization of patterns, the defects of the photomask, which is the original pattern transfer pattern on the wafer to be corrected, are becoming smaller, and high-precision correction is required. Further, in order to correct the light proximity effect and increase the resolution, an optical proximity effect correction (OPC) pattern smaller than the pattern has been introduced, and defects in the OPC pattern smaller than this pattern have to be corrected. In addition to conventional defect correction equipment using lasers and focused ion beams, scratch processing, which is the physical removal of black defects with a diamond probe that takes advantage of the high resolution and position controllability of the atomic force microscope (AFM) (Non-patent Document 1).

  In the conventional AFM scratch processing apparatus, the low magnification was observed with an optical microscope, and the high magnification was observed with an AFM. Even if mask alignment is performed and the defect inspection apparatus and the defect coordinates are linked, there is a deviation of about 10 to 20 μm, and even with the optical microscope, the defect is too small to be found because the defect is too small. Therefore, it must be done with an AFM image that takes time to acquire the image, but even with an AFM image, it is difficult to find a defect with a 40 μm field of view. Scratching was performed after finding defects by observing while changing the location. It took time to locate the defect rather than processing.

  The diamond tip used for processing was worn out during processing, and it was necessary to replace the probe. Whenever the probe was replaced, a dedicated pattern was used to match the center of the optical microscope field of view with the center of the AFM field of view, but this was also a time-consuming task. In addition, even if the field center is aligned as described above, the magnification of the optical microscope is low, so the field center is shifted by about 5 μm from the field center of the AFM. After observing with the visual field and holding the defect at the center, it was observed again with a visual field of about 2 μm, and scratching was performed by increasing the load in the visual field.

  In AFM scratch processing, the surface removed using a specially shaped probe having a vertical cross section is removed so that the black defect touching the pattern is removed. Therefore, depending on the direction of the defect, the mask must be rotated, and each time the mask alignment is performed, the defect inspection device and the defect coordinates are relinked, and the AFM image, which takes time to acquire the image, is searched again for further time. It was over.

  In addition to black defects that are pattern surpluses, there are white defects that are pattern defects in photomasks. In principle, the AFM scratch processing apparatus cannot correct white defects. In this case, the FIB-CVD film or electron beam CVD film using a focused ion beam device (FIB) or electron beam device can be used for correction, but a small film of 0.1 μm or less cannot be attached. There are various problems such as low transmittance due to the halo component, and charge up caused by correcting the photomask, which is an insulator, with charged particles. There was a need for high-precision correction of small defects that could be corrected with

In addition, if an AFM scratch processing device cut out too much black defects when it was corrected, the AFM scratch processing device could not do anything but only removal processing. In this case, the part that was cut too much by the white defect correction function of the FIB or electron beam apparatus is corrected, but it was not possible to correct the defect with a small level that can be corrected by the AFM scratch machine with high accuracy. Conventionally, the AFM scratch processing device operating in the atmosphere, and the FIB and electron beam devices that require vacuum have been installed separately. For this reason, when using both the AFM scratch processing apparatus and the FIB and electron beam apparatus that require vacuum, the sample must be transferred between each apparatus. Each time the sample is transferred, it is necessary to locate the defect in each apparatus. If the AFM scratch processing device and the FIB or electron beam device must be used alternately several times, the number of time of defect location in AFM scratch processing that takes time will increase, which will greatly increase the work time. Become. Also, when using the FIB or the electron beam apparatus, it takes time to wait for evacuation or release to the atmosphere every time, and it is also necessary to re-align the mask every time the mask is replaced.
Y. Morikawa, H. Kokubo, M. Nishiguchi, N. Hayashi, R. White, R. Bozak, and L. Terrill, Proc. Of SPIE 5130 520-527 (2003)

  The present invention is intended to solve the above-described problems, improve the throughput of AFM scratch processing, and correct small white defects with high accuracy even in white defect correction. In addition, if it is cut too much by AFM scratching, it will be possible to repair in a short time.

  In order to solve the above problems, an electron beam apparatus with the advantages of high resolution, short observation time, little damage to the sample during image observation, and the ability to correct white defects and high-precision black defect correction A device that combines the AFM scratch processing machine, which has the advantage of being able to be used. And the following methods are performed using this apparatus.

  After the replacement of the AFM probe, the deepest position of the indentation of the probe formed by pushing the machining probe in the center of the AFM field before replacement is observed with the focused electron beam, and the position and the focused electron The displacement of the probe mounting position is corrected using the distance from the center of the beam field of view as the offset amount of the focused electron beam and the atomic force microscope probe. That is, an offset is given to the scanning range of the AFM or the focused electron beam so that it matches the visual field center of the focused electron beam and the visual field center of the AFM.

  In order to speed up the defect positioning with the AFM scratch machine, the defect is to be corrected by observing the defect with a focused electron beam at high resolution, and the defect is detected with the AFM scratch machine based on the information. Then, the defect is scratched with AFM.

  If a vertical cross-section is required, the surface is used to process the processing probe based on the shape of the processing probe that is pushed in and observed with a focused electron beam. The angle with respect to the X axis or Y axis of the stage is obtained, and the probe mounting angle error is corrected so that the vertical plane is parallel to either the X or Y axis.

  For white defect correction, first, a light-shielding film source gas is supplied to the white defect and a focused electron beam is irradiated to deposit a light-shielding film on the white defect area so that it protrudes from the normal pattern. Is scraped off by AFM scratch processing as well as black defect correction. In this way, small white defects can be corrected with high accuracy.

  When correcting a black defect protruding from a normal pattern film by AFM scratch processing, the part that was cut too much with a focused electron beam while supplying a light shielding film source gas to the place where it was cut too much to penetrate into the pattern film A light shielding film is deposited so that the normal pattern protrudes, and the protruding portion is scraped and repaired with high accuracy by AFM scratch processing in the same manner as the black defect correction.

  By observing with a focused electron beam, it is possible to reduce the number of times of image observation by AFM, which takes 5 to 10 minutes for each positioning after the replacement of the probe, so the replacement of the probe and the subsequent alignment of the probe Can be shortened. A system consisting of a conventional AFM and an optical microscope, which takes about 10 minutes to evacuate and open to the atmosphere, because it uses a device that combines an electron beam and AFM in a vacuum. Compared with, the total correction time can be shortened.

  By locating the defect and determining the required direction of the vertical section (stage rotation direction) with a high-magnification secondary electron image, time-consuming AFM imaging can be omitted, so the evacuation time and open time are Even if it takes, the total correction time can be shortened.

  Since the correction of the deviation of the mounting angle of the vertical surface of the processing probe is also calculated from the secondary electron image of the focused electron beam, the time-consuming AFM imaging that was previously performed can be omitted, reducing the total time. Can do. Conventionally, because the vertical angle of the processing probe is corrected by the stage rotation, and the XY position error is corrected by moving the XY stage, the defect position is corrected by the secondary electron image of the focused electron beam. Since the time-consuming AFM imaging that was performed can be omitted, the total time can be reduced.

  Unlike a single AFM scratch machine, a light-shielding film is attached by electron beam CVD, so white defects can be corrected. Since it is shaved by AFM scratch processing after the light shielding film is attached, small defects can be corrected, and high-accuracy correction similar to AFM scratch black defect correction can be performed.

  Since it is a device that combines a focused electron beam and AFM scratch in a vacuum, it is the same device compared to the case of another conventional device, so the time required for putting in and out the mask and mask alignment can be shortened, and it can be corrected by black defects in AFM scratch processing. It is possible to repair the part that has been shaved excessively in a short time.

  An embodiment of the present invention will be described below.

  FIG. 1 shows a combined electron beam and AFM apparatus used in the present invention. The photomask 3 in which defects are found in the defect inspection apparatus is introduced into the preliminary chamber 11 of the apparatus in which the electron optical system 6 and the atomic force microscope (AFM) head 1 are combined in a container having a vacuum exhaust system 12, and the preliminary exhaust is performed. I do. When the vacuum in the preliminary chamber is evacuated, the photomask 3 is moved to the work chamber 10, the alignment mark of the mask is observed with a high magnification by the focused electron beam 7, and the mask alignment (defect inspection apparatus and coordinate origin alignment) is performed. Alignment marks can be aligned with higher accuracy than when aligned with an optical microscope, and in a shorter time than when aligned with AFM. The stage is moved to a position where there is a defect after mask alignment.

  If the processing probe 2 needs to be replaced, move the XY stage 5 to a position where the AFM head 1 is located, and push the replaced probe into the soft sample at the center of the AFM field before replacement. . Next, the XY stage 5 is moved to the center of the visual field of the focused electron beam 7 to obtain a high-magnification secondary electron image, and the position of the new probe 2 is obtained from the position of the indentation of the probe as shown in FIG. The position of the probe is corrected by correcting the offset amount of the focused electron beam. In other words, the AFM visual field center before and after the probe replacement shifts due to the probe mounting error, but the probe position after the replacement after the probe is pushed by the center of the visual field before the probe replacement is shifted. The scanning range is offset so that the center of the AFM field of view before and after the probe replacement coincides. Since there is no observation process with AFM, the position of the probe can be corrected in a shorter time than before. Since the position is measured with a high-magnification secondary electron image, the alignment accuracy is improved compared to the alignment of the optical microscope and the probe. The amount of mounting angle deviation of the vertical section is also obtained from the shape of the indent.

  Observe the defect with a high-magnification secondary electron image to grasp the shape of the defect. In the case of an isolated black defect, it is processed with a symmetrical processing probe. In the case of a black defect adjacent to the pattern, rotate the rotary stage 4 around an axis perpendicular to the upper surface of the rotary stage 4 so that the surface perpendicular to the sample of the processing probe 2 and the side surface of the defect pattern are parallel. The position of the XY stage 5 is calculated by calculating the correction amount of the XY stage 5 from the rotation angle, and after detecting the defect with the focused electron beam 7, the processing probe 2 having a vertical section is scratched. Remove.

  Since there is a 5 to 20 μm axis shake on the rotary stage, there may be cases in which no defect is found at that position even if the position is corrected by calculating the correction amount of the XY stage 5 from the rotation angle. A conventional AFM scratch machine Then, it took a long time to search for the vicinity of the AFM image, or after re-aligning the mask alignment in the rotated state, the defect was found with the time-consuming AFM image, and then scratch processing was performed. However, in this application, since the defect search after stage rotation correction is performed with the focused electron beam image, which is overwhelmingly shorter than the AFM, the stage rotation correction is performed. Even when the mask alignment is read again in the above state, it can be found in a short time.

  A correction method when the defect is a white defect will be described with reference to FIG. The XY stage 5 is moved so that the white defect 16 comes to the center of the visual field of the focused electron beam. The light shielding film 17 is attached so as to protrude from the white defect 16 by the focused electron beam 7 while flowing the light shielding film source gas from the gas supply system 8. Next, the stage is moved so that the light shielding film 17 comes to the center of the field of view of the AFM, and excess light shielding film and halo component 18 are removed from the light shielding film 17 by AFM scratch processing. Since AFM scratch processing is excellent in height controllability, it is possible to perform processing with little damage to the substrate.

  Even when the black defect is corrected too much by AFM scratch processing, the defect is corrected by the same method as shown in paragraph [0022] for the excessively cut portion. Neither AFM scratching imaging nor focused electron beam imaging can reduce the transmission, so it can be processed repeatedly.

  In the focused electron beam imaging, if contamination accumulates on the photomask substrate (glass substrate) by reacting with the residual gas in the vacuum, the contamination 20 on the glass substrate is contaminated as shown in FIG. By cutting off with AFM scratch processing with the probe 2 which is harder than Nation, it is possible to recover the reduced transmittance due to contamination adhesion.

It is a schematic sectional drawing which best expresses the feature of the present invention. It is explanatory drawing of the probe position alignment method after probe replacement. It is a schematic sectional drawing explaining the correction method in the case of correcting a white defect, or repairing the part cut too much by scratching. It is a schematic sectional drawing explaining the case where the contamination of the glass part attached by the imaging of the focused electron beam is scraped off by AFM scratch processing.

Explanation of symbols

DESCRIPTION OF SYMBOLS 1 AFM head 2 Processing probe 3 Photomask 4 Rotating stage 5 XY stage 6 Electron optical system 7 Focused electron beam 8 Light shielding film raw material supply system 9 Secondary electron detector 10 Work room 11 Preparatory room 12 Vacuum exhaust system 13 Processing probe When the needle is pushed in 14 Light shielding film pattern 15 Glass substrate 16 White defect or scratched part 17 Light shielding film 18 Halo part 19 Contamination on light shielding film 20 Contamination on glass

Claims (3)

A photomask defect correction method using a combined device of a focused electron beam device and an atomic force microscope,
Push processing probe of the atomic force microscope to said photomask, and forming an impression,
Irradiating the indentation with a focused electron beam to obtain an observation image;
Rotating the X-axis or stage for placing the photomask so as to be parallel to the Y axis of the surface and the stage is used from the shape of the indentations before Symbol observation image in the processing of the processing probe, the angular deviation Correcting, moving the X-axis or Y-axis of the stage, and correcting the XY positional deviation ;
Scratching the defects of the photomask with the processing probe.   2. The visual field deviation is corrected by obtaining an offset amount between the observation image of the focused electron beam and the observation image of the atomic force microscope from a positional deviation amount between the indentation and the visual field center of the focused electron beam in the observation image. The photomask defect correction method described in 1. A photomask defect correcting method for correcting white defects by CVD using a focused electron beam,
3. The photomask defect correcting method according to claim 1, wherein the defect is a portion where a shielding film is deposited on the white defect by CVD using the focused electron beam and protrudes from a normal pattern of the shielding film. .

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